An Experimental Study of the Influence of Background Benzo[a]pyrene Concentration on Its Emissions

The study presents an experimental investigation of how the background concentration of benzo(a)pyrene (BaP) affects its mass emissions during fixed-bed coal combustion. The inlet-air benzene-alkylphenols (BaP) level in the referenced laboratory experiment with controlled flue-gas recirculation (FGR) varied from 0.001 to 0.044 µg·m⁻³. We determined the BaP concentration in combustion products by isokinetic aerosol sampling on AFA-HP filters, followed by HPLC analysis. Statistical processing of the experimental data using fourth-order polynomial regression allowed us to obtain an equation for the gain describing the ratio of BaP in flue gases to the initial background. The model's determination coefficient was 0.999, indicating its high predictive ability. It was found that with an increase in the background BaP concentration to 0.03 μg m⁻³, the gain factor value increases by almost an order of magnitude, after which the concentration increase slows. These findings confirm the radical-chain mechanism of secondary polycyclic aromatic hydrocarbon formation and demonstrate that even modest ambient BaP levels significantly distort traditional emission calculations based on zero- background assumption. The derived relationship offers a quantitative tool for adjusting regulatory calculation methods, optimizing recirculation systems, and justifying measures to clean incoming air. Further validation requires passive experiments under natural background air pollution conditions.